Pigs are useful domestic animals which are raised for edible meat, show quick growth and have high conversation rate of grains into meat. However, being quick in growth, they show symptoms such as physiologic anemia particularly at their early stage of growth, frequently causing inhibition of growth and onset of diseases. As a countermeasure, administration of drugs (iron preparations) and administration of various medicines for promoting nutrition are carried out but with no sufficient results. Particularly, injection of iron-dextran and oral administration of iron sulfate and iron fumarate are carried out for the purpose of improving physiologic anemia symptoms at the early stage of growth.
However, although administration of iron preparations has a certain effect in improving physiologic anemia and preventing the disease, it is not sufficient in terms of enhancing the growth. In addition, the oral administration of iron components has problems in that their absorption in the intestines is poor and they spoil taste of feed, and the injection, on the other hand, has problems in that it puts a stress on pigs and takes plenty of time in comparison with oral administration.
It is known that 5-aminolevulinic acids have a herbicide action (JP-A-61-502814, JP-A-4-9360), an insecticide action (JP-A-2-138201), a sensitizing action on photo-dynamic cancer therapy, a plant growth enhancing action (Japanese Patent No. 2,613,136) and the like, but their possibility of enhancing growth of pigs is not known.